The present invention is directed to an air turbine including a stator provided with a guide wheel for moist air and having guide passages placed between guide blades, a rotor provided with a runner and having runner blade passages placed between runner blades, an annular intermediate space between the guide blades of the stator and the runner blades of the rotor, and a control unit for controlling the temperature of the air to be supplied to the guide wheel.
Such an air turbine can be used, for example, in heat pumps, refrigeration equipment, air-drying apparatuses, and equivalent devices.
Outdoor air always contains larger or smaller quantities of water in one, two, or three states. Thus, outdoor air always contains water in a gaseous state (as water vapor), but it may additionally contain water in a liquid state (as mist, fog, drizzle, rain), or in a solid state (as snow, hail). Moreover, water may be present simultaneously in gaseous, liquid and solid states (as a so-called mixed cloud).
When wet or moist air expands rapidly in a curved flow duct from a temperature above the freezing point of water to a temperature considerably below this point, the state of the water contained in the air is changed owing to condensation, sublimation, and/or freezing. All of these changes are based on physical phenomena whose mechanisms are very complicated.
The drops of water following along with the flow are accelerated far more slowly than air, because the density of water is considerably higher than that of air. Under these circumstances, in curved ducts, drops of water run along entirely different paths, as compared with particles of air.
The rapid lowering of the temperature resulting from expansion makes all the small drops of water that follow along with the flow subcooled. Subcooled water is, however, a liquid in an unstable state, for which reason, in a cold flow of air, these drops solidify to snow flakes, whose number and size increase rapidly.
If dry flakes of snow or dry particles of ice meet and strike against a cold duct wall whose temperature is below 0.degree. C., no dangerous formation of ice takes place on the duct wall, because the dry snow flakes and the dry particles of ice do not adhere to the cold wall.
If moist flakes of snow, moist particles of ice or small or large subcooled drops of water meet and strike against a warm duct wall whose temperature is higher than 0.degree. C., dangerous formation of ice does not occur either, for snow or ice does not adhere to a warm and moist wall, but glides along it and is blown off.
On the contrary, should subcooled drops of water meet and strike against a cold duct wall whose temperature is lower than 0.degree. C., dangerous formation of ice would occur. In such a case, a strong and hard layer of ice would be formed, and its thickness would increase rapidly. Such formation of ice can take place only within a temperature range of -10.degree. C. to 0.degree. C.